Thrust reverser assembly

ABSTRACT

A thrust reverser assembly for a gas turbine engine including a core engine, a nacelle surrounding at least a portion of the core engine to define a bypass duct between the nacelle and the core engine, including a translating cowl moveable between a first position and a second position, a blocker door movable between a stowed position and a deployed position. The thrust reverser assembly includes multiple actuator assemblies to both translate the cowl and deploy the blocker door.

BACKGROUND

Turbine engines, and particularly gas or combustion turbine engines, arerotary engines that extract energy from a flow of combusted gasespassing through the engine onto a multitude of turbine blades. Gasturbine engines have been used for land and nautical locomotion andpower generation, but are most commonly used for aeronauticalapplications such as for aircraft, including helicopters. In aircraft,gas turbine engines are used for propulsion of the aircraft. Interrestrial applications, turbine engines are often used for powergeneration.

Thrust reverser assemblies are used within turbine engines to provide areverse thrust, for example, for deceleration. Reverse thrust istypically achieved by deploying a door assembly into a bypass duct whichdiverts air from flowing in an aft direction to flowing in a forwarddirection. The door assembly is deployed with an actuation assembly bymoving a translating cowl to release the door into the bypass duct.Before actuation, it is beneficial for the bypass duct to be free of anyspaces, gaps or other obstructions that may decrease efficiency ofairflow through the bypass duct causing drag.

SUMMARY

In one aspect of the present disclosure, a gas turbine engine,comprising a core engine, a nacelle surrounding at least a portion ofthe core engine; a bypass duct defined by and between the nacelle andthe core engine and defining a fore-to-aft air flow conduit, atranslating cowl moveable between a first position and a secondposition, a cascade element located within the translating cowl when thetranslating cowl is in the first position, a blocker door movablebetween a stowed position, where the blocker door is located within aportion of the nacelle, and a deployed position, where the blocker doorextends into the air flow conduit to deflect air through the cascadeelement, a first actuator assembly mechanically coupled to thetranslating cowl and selectively moving the translating cowl between thefirst and second positions and expose the cascade element when thetranslating cowl is in the second position, and a second actuatorassembly mechanically coupled between the blocker door and one of thenacelle or the cascade element and selectively moving the blocker doorbetween the stowed and deployed positions.

According to a second aspect of the present disclosure, a thrustreverser assembly for a gas turbine engine including a core engine, anacelle surrounding at least a portion of the core engine to define abypass duct between the nacelle and the core engine, including atranslating cowl moveable between a first position and a secondposition, a blocker door movable between a stowed position wherein theblocker door is separated from the bypass duct and a deployed position,where the blocker door extends into the air flow conduit to deflect airthrough the cascade element, a first actuator assembly mechanicallycoupled to the translating cowl and selectively moving the translatingcowl between the first and second positions and expose the cascadeelement when the translating cowl is in the second position, and asecond actuator assembly mechanically coupled between the blocker doorand one of the nacelle or the cascade element and selectively moving theblocker door between the stowed and deployed positions.

According to a third aspect of the present disclosure, a method ofoperating a thrust reverser system for an aircraft, comprising moving atranslating cowl between a first position and a second position,deploying a blocker door from a stowed position to a deployed position,where the blocker door extends into an air flow conduit defined by abypass duct defined by and between the nacelle and a core engine,redirecting bypassed air to exit out through a cascade element, andwherein thrust reverser forces are not applied to the translating cowland the core engine.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIGS. 1A and 1B are isolated sectional views of a prior art example of athrust reverser assembly in a first position 1A and a second position1B.

FIG. 2 is a schematic cross-sectional diagram of a gas turbine enginefor an aircraft including a thrust reverser assembly in a firstposition.

FIG. 3 is a schematic cross-sectional diagram of a gas turbine enginefor an aircraft including a thrust reverser assembly in a secondposition.

FIG. 4 is a perspective view of a portion of the thrust reversalassembly in the second position with a call-out of portion of the thrustreversal assembly.

FIGS. 5A and 5B are isolated sectional views of the thrust reverserassembly in the first position 5A and second position 5B of FIG. 2 andFIG. 3, respectively.

FIG. 6 is an isolated sectional view of the thrust reverser assembly ina sequence of snapshots from the first position to the second position.

DETAILED DESCRIPTION

The described aspects of the present disclosure are directed to a thrustreverser assembly, particularly in a gas turbine engine. For purposes ofillustration, the present disclosure will be described with respect toan aircraft gas turbine engine. It will be understood, however, that thedisclosure is not so limited and can have general applicability innon-aircraft applications, such as other mobile applications andnon-mobile industrial, commercial, and residential applications.

As used herein, the term “forward” or “upstream” refers to moving in adirection toward the engine inlet, or a component being relativelycloser to the engine inlet as compared to another component. The term“aft” or “downstream” refers to a direction toward the rear or outlet ofthe engine relative to the engine centerline.

Additionally, as used herein, the terms “radial” or “radially” refer toa dimension extending between a center longitudinal axis of the engineand an outer engine circumference.

It should be further understood that “a set” can include any number ofthe respectively described elements, including only one element.

All directional references (e.g., radial, axial, proximal, distal,upper, lower, upward, downward, left, right, lateral, front, back, top,bottom, above, below, vertical, horizontal, clockwise, counterclockwise,upstream, downstream, aft, etc.) are only used for identificationpurposes to aid the reader's understanding of the present disclosure,and do not create limitations, particularly as to the position,orientation, or use of the aspects described herein. Connectionreferences (e.g., attached, coupled, connected, and joined) are to beconstrued broadly and can include intermediate members between acollection of elements and relative movement between elements unlessotherwise indicated. As such, connection references do not necessarilyinfer that two elements are directly connected and in fixed relation toone another. The exemplary drawings are for purposes of illustrationonly and the dimensions, positions, order and relative sizes reflectedin the drawings attached hereto can vary.

Deploying a blocker door 1 into a bypass duct 2 is known in the priorart as illustrated in FIG. 1A and FIG. 1B and will be briefly describeherein to give reference to problems faced by the prior art, which willlater be used to explain benefits of the present disclosure. In theprior art, the hinged blocker door 1 can be mounted within a nacelle 3and coupled to a pivoting arm 4 where the pivoting arm 4 is furthermounted to an inner core cowl 5 providing a narrowing of the bypass duct2. When deployed the blocker door 1 provides a thrust reversal effect ofredirecting bypass air from an air conduit 6 through a cascade element7. As illustrated in FIG. 1A, when the blocker door 1 is in a stowedposition, the pivoting arm 4 remains in the bypass duct 2 which cancreate drag or force acting opposite the relative motion of an engine 10during operation. As little or no drag is desirable, the pivoting arm 4creates inefficiency, which causes more fuel to be burned than wouldotherwise be necessary.

FIG. 2 schematically represents a gas turbine engine 10 including anacelle 12 surrounding at least a portion of a core engine 14. Theengine 10 has a generally longitudinal extending axis or centerline 36extending forward to aft. A fan assembly 16 located in front of the coreengine 14 includes a spinner nose 18 projecting forwardly from an arrayof fan blades 20.

The core engine 14 is schematically represented as including ahigh-pressure compressor 22, a combustor 24, a high-pressure turbine 26and a low-pressure turbine 28. A large portion of the air that entersthe fan assembly 16 is bypassed to the rear of the engine 10 to generateadditional engine thrust. The bypassed air passes through anannular-shaped bypass duct 30 defining a fore-to-aft air flow conduit 31between the nacelle 12 and an inner core cowl 32, and exits the bypassduct 30 through a fan exit nozzle 34. The inner core cowl 32 defines theradially inward boundary of the bypass duct 30, and provides a smoothtransition surface to a primary exhaust nozzle 38 that extends aft fromthe core engine 14. The nacelle 12 defines the radially outward boundaryof the bypass duct 30. The bypassed fan air flows through thefore-to-aft air flow conduit 31 before being exhausted through the fanexit nozzle 34.

The nacelle 12 can include three primary elements that define theexternal boundaries of the nacelle 12: an inlet assembly 40, a fan cowl42 interfacing with an engine fan case that surrounds the fan blades 20,and a thrust reverser assembly 44 located aft of the fan cowl 42. Thethrust reverser assembly 44 includes three primary components: atranslating cowl 50 mounted to the nacelle 12 and moveable between afirst position (FIG. 2) and a second position (FIG. 3), a cascade 52schematically represented within the nacelle 12, and blocker doors 54adapted to be pivotally deployed from the stowed positions shown in FIG.2. The blocker doors 54 are radially inward from the cascade 52. Whiletwo blocker doors 54 are shown in FIG. 2, a set of blocker doors 54 aretypically circumferentially spaced around the nacelle 12.

FIG. 3 is a second schematic representation of the gas turbine engine 10with the thrust reverser assembly 44 in the deployed position. Thetranslating cowl 50 has been selectively moved in the aft direction 58between a first position 46 (shown in phantom) and a second position 48.The movement of the translating cowl 50 in the aft direction 58 canexpose the cascade element 52.

The cascade element 52 is a fixed structure of the nacelle 12, meaningthat the cascade 52 does not move during the operation of the thrustreverser assembly 44. The cascade element 52 can have deflecting devicesor thrust reverser profiles to direct bypassed air exiting 56 forward ofthe engine 10 when the thrust reverser assembly 44 is in the deployedposition.

The blocker door 54 is adapted to deploy from the stowed position, shownin FIG. 2, to the fully deployed position shown in FIG. 3. A link arm 62can be coupled to the blocker door 54 to aid in moving the blocker door54 between the stowed position (FIG. 2) and the deployed position, wherethe blocker door 54 extends into the air flow conduit 31. The inner corecowl 32 of the core engine 14 is also part of the thrust reverserassembly 44. The fore end 45 of the blocker door 54 is pivoted towardthe inner core cowl 32 such that the fore end 45 is adjacent the innercore cowl 32 when the blocker door 54 is fully deployed causing bypassedair within the bypass duct 30 to be diverted through the exposed cascade52 and thereby provide a thrust reversal effect. It should be noted thatthe inner core cowl 32 as described herein provides a smooth and linearpathway for the fore-to-aft air flow conduit 31 wherein the smoothtransition surface path provided by the inner core cowl 32 transitionstowards the exhaust nozzle 38 without first forming a narrow path as isillustrated in the prior art (FIG. 1).

FIG. 4 is a perspective view of a portion of the thrust reversalassembly 44 with the circumferentially spaced blocker doors 54 in thedeployed position. A first actuator assembly 60 is mechanically coupledto the translating cowl 50 to selectively move the translating cowl 50from the first position 46 (FIG. 2) to the second position 48 when asignal from a controller is received and before the blocker doors 54 aredeployed. The first actuator assembly 60 can comprise a sliding portion64 received within a body of a linear actuator 66 that can be mounted toa sliding ring 68 of the cascade element 52. The sliding portion 64 issecured at a leading end to a fixed structure 65 that can be mounted toan inner wall 72 of the translating cowl 50. Multiple actuatorassemblies for translating the translating cowl 50 aft can becircumferentially arranged and mounted to the cascade element 52, or atany suitable location within the nacelle 12.

A second actuator assembly 70, independently operable from the firstactuator assembly 60, is illustrated in more detail in the call outportion of FIG. 4. The second actuator assembly 70 has been illustratedas including three main components: the link arm 62 coupled to thesliding ring 68 that is further coupled to a linear actuator 74. Thelinear actuator 74 may be any suitable type of actuator that creates alinear output motion. It will be understood that this need not be thecase and that the second actuator assembly 70 can be formed and coupledto the blocker door 54 in any suitable manner. It will be furtherunderstood that both the linear actuator 66 and the linear actuator 74can be pneumatic, hydraulic or electrically driven. The electricallydriven approach can include reduced system complexity and increasedcontrollability.

Each blocker door 54 can be connected to a fixed portion 76 of thecascade element 52 with a rotating element 77 mechanically coupled tothe linear actuator 74. Alternatively the fixed portion 76 could be partof the nacelle 12 while still located aft of the cascade element inorder to maintain a pathway for bypassed air 56 so as not to impartunnecessary forces on the translating cowl 50.

The link arm 62 is pivotally mounted to the blocker door 54 and thesliding ring 68 with, for example but not limited to, a clevis mountingbracket or any other suitable pivoting bracket known in the art. Thelink arm 62 can be formed from steel and when in the stowed position(FIG. 2) is folded in and up behind the blocker door 54 next to thecascade element 52.

The first actuator assembly 60 moves from the first position 46 when thesliding portion 64 slides aft and pushes the translating cowl 50 to thesecond position 48. In the same manner, the sliding portion 64 can slideforward into the body of the linear actuator 66 pulling the translatingcowl from the second position 48 to the first position 46 when a secondsignal is received from the controller under conditions where slowing orbraking of the aircraft is no longer necessary.

The output of the linear actuator 74 determines the movement of thecorresponding parts of the second actuator assembly 70. Morespecifically, in order to rotate the blocker door 54 from the stowedposition, where the blocker door 54 is located within a portion of thenacelle 12, to the deployed position, the linear actuator 74 slidesparallel to the cascade element 52 along a slideable element 78simultaneously bringing the sliding ring 68 towards the fixed portion76. Movement of the sliding ring 68 towards the fixed element 76 causesthe link arm 62 to move from a parallel position between the blockerdoor 54 and the cascade element 52 to an angled position where theblocker door 54 is nearly perpendicular to the fixed cascade element 52.

In the second position 48, the cascade element 52 is fully exposed. Thecascade element 52 can include a plurality of outlets 82 housing thedeflecting devices and through which the bypass air 56 can pass.

The rotating and sliding joints of the blocker door 54 are geometricallyand physically designed to provide a desired sequence and rate ofdeployment for the blocker doors 54. In the deployed position, multipleblocker doors 54 can be configured to interface together to yield adesired percentage of duct blockage, which can be further optimized byseals provided along the edges of the blocker doors 54.

FIG. 5A schematically illustrates a cross sectional view of the thrustreverser assembly 44 when in the stowed position. When compared to FIG.4A, a benefit of the design described herein of allowing bypass air toflow through the bypass air conduit 31 free from any obstructions orturns becomes apparent. In turn a clear bypass air duct 30 decreasesdrag and increases fuel efficiency.

From FIG. 5B, it can be appreciated that, when fully deployed, theblocker door 54 extends across the entire, substantially the entire, oralmost the entire, radial width of the bypass duct 30 and causesbypassed air within the bypass duct 30 to be diverted through theexposed cascade element 52 and thereby provide a thrust reversal effect.Redirecting the bypassed air into a forward direction produces a forcein the opposite direction of travel to ensure deceleration.

Prior to translation of the translating cowl 50 (e.g., while the thrustreverser assembly 44 is not in use), the stowed blocker door 54 ispositioned radially inward of the cascade 52, and both the cascade 52and blocker door 54 are completely concealed by the translating cowl 50.

More particularly, the cascade 52 and blocker door 54 are containedwithin a cavity 80 defined between radially inner and outer walls 72, 84of the translating cowl 50, such that the radially inner wall 72 of thetranslating cowl 50 completely separates the cascade 52 and blocker door54 from the bypass duct 30. The inner wall 72 of the translating cowl 50defines a portion of the radially outer flow surface of the bypass duct30. The blocker door 54 does not define any portion of the radiallyouter flow surface of the bypass duct 30 during normal engine operation,and therefore does not create surface interruptions (gaps and steps) orcause duct leakage. Furthermore, the blocker door 54 is not exposed todamage and wear-inducing conditions during normal in-flight engineoperations. Another advantage is that the entire inner wall 72 of thetranslating cowl 50 can incorporate an uninterrupted acoustic treatment(not shown) of its entire surface area to promote increased engine noiseattenuation.

In FIG. 6 a sequence of snapshots of a portion of the gas turbine engine10, when the thrust reverser assembly 44 is moved between the firstposition 46 and the second position 48 is illustrated. This includes anillustration of translation of the translating cowl 50 by the firstactuator assembly 60 along with the corresponding stowed and deployedpositions of the blocker door 54 as caused by the second actuatorassembly 70. While the second actuator assembly 70 is operableindependent of the first actuator assembly 60, movement of the secondactuator assembly 70 is dependent on the extent to which the firstactuator assembly 60 has moved the translating cowl 50 from the firstposition 46 to the second position 48. Only when the first actuatorassembly 60 has substantially completed translation of the translatingcowl 50 or translated to an extent that the blocker door deployment willnot be hindered, will the second actuator assembly 70 begin deployment.

The controller module (not shown) can be operably coupled to the thrustreverser assembly 44 to control its operation. The controller canreceive a signal from a user, for example a pilot of an aircraft, whenthrust reverser force is necessary to slow or brake the aircraft and asecond signal when thrust reverser forces are no longer necessary. Thesignal can be sent to the first actuator assembly 60 and then to thesecond actuator assembly 70 or both simultaneously. As described herein,the movement of each actuator assembly 60, 70 is dependent on the otherin that when a signal is received from the controller, the firstactuator assembly 60 translates the translating cowl 50 and then thesecond actuator assembly 70 deploys the blocker door 54. Upon receivingthe second signal, the second actuator assembly 70 stores the blockerdoor 54 and the first actuator assembly 60 translates the translatingcowl 50 to a closed position. It will be understood that the controllermodule can include one or more processors to operate the movement of thethrust reverser assembly 44.

FIG. 6 pictorially illustrates a method 200 of operating a thrustreverser system such as the thrust reverser assembly 44. The method 200includes the thrust reverser assembly 44 in a non-use position at 202and first moving 204 and 206 of the translating cowl 50 in the aftdirection 58. More specifically, at 204 the first actuator assembly 60pushes the translating cowl 50 to the second position 48, as shown at206, which leaves the cascade 52 exposed. Then upon completion of movingthe translating cowl 50 aft, deploying the blocker door 54 from a stowedposition, illustrated at 208, to a deployed position, shown at 212,commences. The blocker door is shown at a partially extended position at210. When the thrust reverser assembly 44 is at the use position asillustrated at 212, any bypass airflow in the bypass duct 30 isredirected, as illustrated by arrows 56, to exit out through the cascadeelement 52.

It should be appreciated that the operation of the blocker doors andtheir guided and rotating connections are not dependent on anyparticular type of cascade design, and in fact the embodiments of thepresent disclosure could be installed in a non-cascade thrust reverserassembly design in which the bypassed air is diverted from the bypassduct through openings of various configurations. Furthermore, whereasthe blocker door 54 is shown with a rigid construction that does notintentionally bend, flex or fold during its deployment, blocker doorshaving any of these capabilities are also within the scope of thepresent disclosure. It should be further understood that an extendedlength blocker door or folding door that extends as it is deployed canbe utilized to provide a blocker door that, when deployed, is capable ofextending into the external air flow to provide additional retardingdrag. Finally, it should also be appreciated that the thrust reverserassembly 44 and its individual components can be constructed of variousmaterials, including metallic, plastic and composite materials commonlyused in aerospace applications and fabricated by machining, casting,molding, lamination, etc., and combinations thereof.

In any of the above various aspects, a protective coating, such as athermal barrier coating, or multi-layer protective coating system can beapplied to the cowls or engine components.

The various aspects of systems, methods, and other devices related tothe present disclosure herein provides an improved thrust reverserassembly, particularly in a fan cowl. Conventional thrust reverserassemblies utilize a blocker door coupled to an actuation system.However, the actuation system must have enough structural integrity tosupport the load created by the force of the airflow against the blockerdoor as it opens within the bypass duct, requiring a larger actuationsystem. In the present disclosure, any thrust reverser forces are notapplied to the translating cowl or the core engine. As such, a smallerload is borne by the actuation system, allowing a lighter, smalleractuation system, decreasing the weight of the system and creatingadditional room within the nacelle structure.

Benefits include low air drag and a higher proficient ratio, around 50%,of acoustic area to wetted area near 50% due to the removal of a linkarm and any steps or gaps in the fan duct conduit. Removal of the linkarm within the fan duct and replacement with a smaller link armmechanism decreases the overall weight of the thrust reversal assembly.The disclosed thrust reverser assembly also prevents thrust reverserforces from being unnecessarily applied to the translating cowl or corecowl.

The disclosed thrust reverser assembly reduces part count, simplifiesstructure, and can be applied to a wide range of engines, including butnot limited to all high-bypass commercial and military engines. Thedisclosed assembly also provides for good access to all components whichallows for efficient repair time when necessary.

This written description uses examples to disclose the invention,including the best mode, and to enable any person skilled in the art topractice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and can include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A gas turbine engine, comprising: a core engine;a nacelle surrounding at least a portion of the core engine; a bypassduct defined by and between the nacelle and the core engine and defininga fore-to-aft air flow conduit; a translating cowl moveable between afirst position and a second position; a cascade element located withinthe translating cowl when the translating cowl is in the first position;a blocker door movable between a stowed position, where the blocker dooris located within a portion of the nacelle, and an deployed position,where the blocker door extends into the air flow conduit to deflect airthrough the cascade element; a first actuator assembly mechanicallycoupled to the translating cowl and selectively moving the translatingcowl between the first and second positions and expose the cascadeelement when the translating cowl is in the second position; and asecond actuator assembly mechanically coupled between the blocker doorand one of the nacelle or the cascade element and selectively moving theblocker door between the stowed and deployed positions.
 2. The gasturbine engine of claim 1 wherein the second actuator assembly isoperable independently of the first actuator assembly.
 3. The gasturbine engine of claim 1 wherein the blocker door is rotatably mountedto a portion of the cascade element.
 4. The gas turbine engine of claim1 wherein the second actuator assembly further comprises a linearactuator.
 5. The gas turbine engine of claim 4 wherein the secondactuator assembly further comprises a slideable element operably coupledto the linear actuator and where the slideable element is slideablealong at least a portion of a length of the cascade based on outputprovided by the linear actuator.
 6. The gas turbine engine of claim 5wherein the second actuator assembly further comprises a link armmechanically coupling the slideable element to the blocker door.
 7. Thegas turbine engine of claim 5, further including multiple blocker doorsradially spaced about the core engine and wherein the multiple blockerdoors are operably coupled to the slideable element.
 8. A thrustreverser assembly for a gas turbine engine including a core engine, anacelle surrounding at least a portion of the core engine to define abypass duct between the nacelle and the core engine, including: atranslating cowl moveable between a first position and a secondposition; a blocker door movable between a stowed position wherein theblocker door is separated from the bypass duct and an deployed position,where the blocker door extends into the air flow conduit to deflect airthrough the cascade element; a first actuator assembly mechanicallycoupled to the translating cowl and selectively moving the translatingcowl between the first and second positions and expose the cascadeelement when the translating cowl is in the second position; and asecond actuator assembly mechanically coupled between the blocker doorand one of the nacelle or the cascade element and selectively moving theblocker door between the stowed and deployed positions.
 9. The thrustreverser assembly of claim 8, further comprising a fixed cascade elementlocated within the translating cowl when the translating cowl is in thefirst position.
 10. The thrust reverser assembly of claim 8 wherein thesecond actuator assembly is operable independently of the first actuatorassembly.
 11. The thrust reverser assembly of claim 8 wherein theblocker door is rotatably mounted to a portion of the cascade element.12. The thrust reverser assembly of claim 8 wherein the second actuatorassembly further comprises a linear actuator.
 13. The thrust reverserassembly of claim 12 wherein the second actuator assembly furthercomprises a slideable element operably coupled to the linear actuatorand where the slideable element is slideable along at least a portion ofa length of the cascade based on output provided by the linear actuator.14. The thrust reverser assembly of claim 13 wherein the second actuatorassembly further comprises a link arm mechanically coupling theslideable element to the blocker door.
 15. The thrust reverser assemblyof claim 13, further including multiple blocker doors radially spacedabout the core engine.
 16. The thrust reverser assembly of claim 8wherein the multiple blocker doors are operably coupled to the slideableelement via separate link arms.
 17. The thrust reverser assembly ofclaim 8, further comprising an uninterrupted acoustic treatment on aninner wall of the translating cowl.
 18. A method of operating a thrustreverser system for an aircraft, comprising: moving a translating cowlbetween a first position and a second position; deploying a blocker doorfrom a stowed position to a deployed position, where the blocker doorextends into an air flow conduit defined by a bypass duct defined by andbetween the nacelle and a core engine; redirecting bypassed air to exitout through a cascade element; and wherein thrust reverser forces arenot applied to the translating cowl and the core engine.
 19. The methodof claim 18 wherein the blocker door in the stowed position is locatedwithin a portion of the nacelle or the translating cowl.
 20. The methodof claim 19 wherein no link arms are located in the bypass duct when theblocker door is located in the stowed position.